The "fundamental value of the business" is not an exact amount. The day-to-day variation in price (to the extent it isn't correlated to the index, anyway) can generally be viewed as a side-effect of uncertainty about what it actually is. In some sense, the value is unknowable, because it is a function of other things that are not knowable (e.g. future interest rates). So there's a measure of "other people would find an argument for this valuation reasonable", even for the fundamentals.

In any event, this sort of news generally does not move the fundamental value of the business in a way that exceeds the "uncertainty band", so pretty much all of the active trading is necessarily in anticipation of how others will view the news.

This is in contrast to e.g. merger offers, which are much more about the actual value of the business (which has suddenly become very concrete and precise), and not trying to judge the reaction of others. But major events like that are a small minority.